1. Technical Field of the Invention
The present invention relates generally to rotors for rotating electrical machines, such as electric generators and motors, and methods of manufacturing the rotors.
More particularly, the invention relates to rotors for automotive alternators, which include Lundell-type pole cores as rotor cores, and their manufacturing methods.
2. Description of the Related Art
Conventionally, a rotor for an automotive alternator generally includes a pair of Lundell-type pole cores as rotor cores. The pole cores are press-fit on a shaft of the rotor so that they are opposed to each other in the axial direction of the shaft, forming a hollow space therebetween. The rotor further includes a field coil that is received in the space formed between the pole cores, and fit on the shaft via an insulating bobbin.
The insulating bobbin has a cylindrical body and a pair of flanges. The body is fit on the pole cores, and has the field coil wound thereon. The flanges extend radially outward from opposite axial ends of the body, respectively. Moreover, one of the flanges has securing portions integrally formed therewith for securing (or hooking) both a winding start lead and a winding end lead of the filed coil, so as to prevent the field coil from being loosened.
There have been proposed various structures of the securing portions for securing the leads of the field coil, such as those disclosed in Japanese Patent First Publications No. 2001-37180, No. 2002-335661, and No. 2000-125528, English equivalents of which are respectively U.S. Pat. Nos. 6,172,434, 6,784,577, and 6,114,786.
For example, FIGS. 11A and 11B show part of a rotor 100 for an automotive alternator, which is disclosed in Japanese Patent First Publication No. 2001-37180.
As shown in FIG. 11A, the rotor 100 includes a shaft 101, a pair of Lundell-type pole cores 102 press-fit on the shaft 101, an insulating bobbin 103 fit on the pole cores 102, and a field coil 104 that is wound around the insulating bobbin 103 and received in a hollow space formed between the pole cores 102 along with the insulating bobbin 103. The insulating bobbin 103 has a cylindrical body 105, around which the field coil 104 is wound, and a pair of flanges 106 that extend radially outward from opposite axial ends of the body 105, respectively.
Moreover, one of the flanges 106 has a pair of stays 108 integrally formed therewith for respectively securing both the winding start and winding end leads 107 of the filed coil 104. The stays 108 are symmetrically formed with respect to the shaft 101, and have the same structure. Therefore, for the sake of simplicity, only one of the stays 108 which is used to secure (or hook) the winding end lead 107 of the field coil 104 will be described hereinafter with reference to FIGS. 11A and 11B.
The stay 108 is fit in a root portion 109 of a corresponding one of the pole cores 102; the root portion 109 is formed, between an adjacent pair of claw portions of the pole core 102, into a V-shaped groove. Moreover, the stay 108 is integrally formed with an E-shaped winder 110, around which a proximal portion of the lead 107 is wound. The lead 107 is then guided by a groove 111 formed in the stay 108, so as to extend in the axial direction of the shaft 11 along the surface of the root portion 109. After reaching an axial end face of the pole core 102, the lead 107 is further guided by a groove 112 formed in the axial end face, so as to extend radially inward to have its distal portion wound around a terminal (not shown); the terminal is electrically connected to a slip ring (not shown) provided on the shaft 101. Furthermore, an intermediate portion of the lead 107 is covered by an insulating tube 113, and the insulating tube 113 is bonded to both the root portion 109 and the groove 112 of the pole core 102 by an adhesive 114.
In operation of the alternator, the rotor 100 rotates about the shaft 101, creating a magnetic attraction between the pole cores 102 and a stator core (not shown) of the alternator. The magnetic attraction causes the pole cores 102 to vibrate. Further, with the vibration of the pole cores 102, the insulating bobbin 103 are repeatedly attached to and detached from the pole cores 102 in the axial direction of the shaft 101: Consequently, the lead 107 comes to receive, from the root portion 109 and a shoulder portion 115 of the pole core 102, both a centrifugal force and a repeated tensile force.
Further, since movement of the lead 107 is restricted by both the stay 108 and the insulating tube 113 that is bonded to the pole core 102, the tensile force will concentrate on a portion of the lead 107 between the stay 108 and the shoulder portion 115 of the pole core 102. As a result, the portion of the lead 107 may be broken due to the concentration of the tensile force thereon.
In addition, as illustrated in the fourth embodiment of Japanese Patent First Publication No. 2001-37180, the insulating tube 113 may be extended to cover all the portion of the lead 107 between the stay 108 of the insulating bobbin 103 and the shoulder portion 115 of the pole core 2, so as to relax the concentration of the tensile force on the portion. However, in this case, depending on the quality of applying the adhesive 114, the insulating tube 113 may be securely bonded to the pole core 102, but may not be securely bonded to the stay 108 of the insulating bobbin 103. As a result, it would be difficult to achieve the intended effect of relaxing the concentration of the tensile force on the portion of the lead 107.
FIG. 12A shows part of a rotor for an automotive alternator, which is disclosed in Japanese Patent First Publication No. 2002-335661. FIG. 12B shows part of a variation of the rotor of FIG. 12A. FIGS. 13A-13C together show hook portions formed in the rotor of FIG. 12A.
As shown in FIGS. 12A and 13A-13C, in the rotor, a flange 106 of an insulating bobbin is formed with a first hook portion 121 and a second hook portion 122. The first hook portion 121 is provided to direct a lead 107 of a field coil 104 to extend in an opposite direction to the winding direction of the field coil 104. The second hook portion 122 is provided to guide the lead 107.
The lead 107 extends from a winding portion of the field coil 104, and is bent by the first hook portion 121 at an acute angle. Thereafter, the lead 107 is guided by the second hook portion 122 to extend first radially inward and then axially outward. An insulating tube 113 is mounted on the lead 107 from a distal end of the lead 107 to the second hook portion 122. The insulating tube is further bonded to the second hook portion 122 by resin impregnation (i.e., adhesive) 114.
With the above configuration, it is possible to firmly secure the lead 107 by simply hooking it on the first and second hook portions 121 and 122. Further, since the lead 107 is bonded to the flange 106 by the resin impregnation 114, it is possible to reliably prevent the lead 107 from being loosened and from being broken due to a centrifugal force acting thereon during operation.
However, with the above configuration, is may be difficult to accurately mount the insulating tube 113 onto a desired section of the lead 107. Consequently, it may be difficult to secure a desired boding strength of the insulating tube 113 after applying the resin impregnation 114.
In addition, in the variation of the rotor shown in FIG. 12B, the insulating tube 113 is mounted on the lead 107 from the distal end of the lead 107 over the first hook portion 121. However, in even this case, it may still be difficult to accurately mount the insulating tube 113 onto a desired section of the lead 107; thus, it may be difficult to secure a desired bonding strength of the insulating tube 113 after applying the resin impregnation 114.